1. Field of the Invention
The present invention relates to an optical position detector which detects a position by using a triangulation method.
2. Description of the Prior Art
Conventionally, optical position detectors have widely used a triangulation method Due to the low cost and simple structure, they have wide application as sensors for camera auto-focusing. FIG. 5 shows a position detection method by triangulation in a conventional optical position detector as disclosed, for example, in the publication "Needs and Seeds of Optical Instrumentation" (P.167) by the Study and survey Committee for Optically Applied Measuring Technology, the Society of Weights and Measures. In FIG. 5, reference numeral 101 denotes a light source such as a laser which emits a parallel beam, and the light source is not provided with a lens for light projection. 102 is an image formation lens, 103 is a position detection element (for example PSD (position sensitive device) or the like). In this optical position detector, either the image pickup system is oblique to the displacement direction of the detected surface 104 or the incident direction of light is inclined against the displacement direction.
The operation of the conventional optical position detector will now be explained.
When the detected surface 104 is displaced from a reference position, the prospect angle with respect to the image formation lens 102 of the spot on the detected surface 104 varies. Since the image position on the position detecting element 103 varies in response to the variation of the prospect angle, the position of the detected surface 104 can be calculated.
Since conventional optical position detectors are constructed as above, when a compact semiconductor laser is used as a light source, a collimator lens must be provided, and when the light source 101 is a gas laser, the laser size must be inherently large though a lens system is not necessary. In other words, in the conventional optical position detector using a triangulation method, since a general image forming lens 102 is used for convergence of light and image formation, there is a limit to the degree to which the device can be miniaturized
Furthermore, an optical position detector which uses a bar shaped lens having uni-axial focussing operation and an optical fiber as an optical guide is disclosed, for example, in the publication JP-A 10-9813. However, the optical position detector also has a problem that there is a limit to the degree to which the device can be miniaturized, if it is required to obtain an excellent detection characteristic at long measurement distance.